Characteristically plasticized polyvinyl chloride compositions, when in the form of molded articles, have relatively low toughness and crack propagation resistance at low temperatures.
In recent years, rigid polyblends of polyvinyl chloride (PVC) with rubbers and grafted rubbers have been developed to improve the toughness of PVC compounds. Rigid PVC polyblends with rubbers grafted with styrene and acrylonitrile were disclosed by Hayes in U.S. Pat. No. 2,802,809 granted Aug. 13, 1957. More sophisticated grafted rubbers have been developed for rigid PVC polyblends to improve their transparency for rigid vinyl bottles as disclosed by Beer in U.S. Pat. No. 3,636,138 granted July 18, 1972.
Currently, there is a great need for molded shoe parts, in particular, the soles and heels to provide shoe components that are economically manufactured and fabricated into shoes. A recent development has been the Unit-Sole or unitary sole and heel injection molded in the shape of a sole and heel. Such Unit Soles are combined with molded or fabricated uppers by adhesives to provide an attractive article of footwear at low fabricating costs. Unitary sole-heel articles have been molded of plasticized vinyl compounds but such moldings have relatively low flex crack endurance and low coefficients of friction for shoe soles. Block copolymers of butadiene and styrene have been used extensively but have relatively poor moldability and pliability and dimensional stability along with poor adhesion having to be chlorinated to establish adequate bonds. Polyurethane moldings have been developed that have high flex crack endurance but slow molding rates.
There has now been discovered a new and very useful plasticized polyvinyl chloride polyblend composition that can readily be injection molded into articles that are tough and resilient yet have high flex crack endurance over a wide temperature range. Such articles can be unitary shoe-heel moldings or other articles requiring tough, resilient, rubbery properties such as bumper guards and other impact absorbing elements.
These unusual flex-crack properties are gained without substantially affecting various other physical properties of the polyblend such as tensile strength, elongation to fail, impact strength and the like as compared to the known prior art materials cited and in particular plasticized vinyls or semi-rigid vinyls. The polyblends provide a superior coefficient of friction, low mold shrinkage, good adhesion, greater flex crack resistance at low temperatures and excellent moldability. Within the properties needed the composition can be varied providing a range of properties such as hardness and resiliency that allows the composition to be tailored to exacting uses.
The present invention relates to a polymer composition comprising:
A. a polyvinyl chloride polymer being characterized by having an inherent viscosity of from about 0.7 to 1.5 in a 0.2 weight percent cyclohexanone solution at about 25.degree. to 30.degree.C., said polyvinyl chloride polymer comprising a polymer selected from the group consisting of homopolyvinyl chloride and polyvinyl chloride copolymers having up to 25 weight percent of another ethylenically unsaturated comonomer polymerizable therewith, PA1 B. a butadiene-styrene rubbery substrate having a butadiene content of 68 to 95 percent by weight and a styrene content of 5 to 32 percent by weight based on the total weight of the butadiene-styrene rubbery substrate which rubbery substrate is further characterized as having a particle size in the range of from 0.06 to 0.2 micron, a gel content in the range of from 40 to 95 percent, a swelling index in the range of from 10 to 40, and a second order transition temperature (Tg) less than -40.degree.C. PA1 C. a superstrate grafted onto the rubber substrate which superstrate comprises: PA1 D. a plasticizer system for said polymer composition, said plasticizer system being present in a sufficient amount to produce in said polymer composition after such is heat fused at a temperature of from about 120.degree. to 215.degree.C., a Shore A hardness value in the range of from about 45 to 95 at about 23.degree.C., PA1 E. a stabilizer system for said polymeric composition, said stabilizer system being present in such amounts as to substantially prevent the thermal degradation of said polymeric composition during heat fusion for 5 to 15 minutes at temperatures in the range of from about 120.degree. to 215.degree.C., and PA1 F. a lubricant system present in such amounts as to permit the release of said polymeric composition from a heated solid surface after said polymeric composition has been heat fused at temperatures in the range of from about 120.degree. to 215.degree.C.
1. the polymerization product of a first polymerizable monomer composition comprising: PA2 2. a second polymerizable monomer composition comprising from 55 to 85 percent by weight of an ethylenically unsaturated nitrile monomer selected from the group consisting of acrylonitrile and mixtures of acrylonitrile and methacrylonitrile which contains up to 20 percent by weight of methacrylonitrile based on the total weight of acrylonitrile and methacrylonitrile and from 15 to 45 percent by weight of a monovinylidene aromatic hydrocarbon monomer wherein the percent by weight is based on the total weight of the monomers in the second polymerizable monomer mixture;
a. from 0.1 to 2 percent by weight of a nonconjugated diolefin monomer, PA3 b. from 20 to 30 percent by weight of an ethylenically unsaturated nitrile selected from the group consisting of acrylonitrile, and mixtures of acrylonitrile and methacrylonitrile which contain up to 20 percent by weight of methacrylonitrile; PA3 c. from 40 to 60 percent by weight of a vinylidene aromatic hydrocarbon monomer selected from the group consisting of styrene and alpha methyl styrene, PA3 d. from 20 to 50 percent by weight of methyl methacrylate; and
wherein the grafted superstrate contains a total of at least 40 percent by weight ethylenically unsaturated nitrile monomer and wherein the ratio of grafted superstrate to substrate is in the range of from 15-200:100,